The present invention relates to a control apparatus for controlling a traction motor equipped in an vehicle, such as an electric car and a hybrid car, the traction motor generating a driving torque necessary for running the automobile.
Hybrid vehicles and electric vehicles driven by secondary cells or fuel cells are representative vehicles using an electromotive torque.
To realize a vehicle traveling control based on control of this kind of traction motor, a traction motor equipped vehicle usually includes a motor control apparatus and a vehicle electronic control apparatus (i.e. a vehicle ECU). The motor control apparatus is capable of controlling a motor voltage applied to a traction motor (i.e. an AC motor). The vehicle electronic control apparatus is capable of calculating a torque command value based on information entered from an accelerator pedal and a brake pedal and transmitting the calculated torque command value to the motor control apparatus. Furthermore, the motor control apparatus has a current command value calculating section, a voltage command value calculating section, and an inverter section. The current command value calculating section calculates a current command value based on a torque command value and a rotational speed of the traction motor. The voltage command value calculating section calculates a voltage command value based on a difference between a detect current of the traction motor and a current command value, and outputs the calculated voltage command value to the traction motor so as to reduce the difference to 0. The inverter section applies a motor voltage corresponding to the calculated voltage command value to the traction motor. This kind of motor control apparatus is, for example, disclosed in the Japanese patent application laid-open No. 2003-009573.
However, according to the above-described conventional vehicle using an electromotive torque, if a traction load entered to wheels of the vehicle suddenly changes, drivability of the vehicle will be worsened due to an abrupt change in the output, especially in the rotational speed, of the traction motor driving these wheels.
Furthermore, according to the conventional vehicle using an electromotive torque, the vehicle ECU calculates a required torque command value in accordance with a vehicle speed or a motor speed and transmits the calculated torque command value to the motor control apparatus. Then, the motor control apparatus executes a current feedback control for equalizing a motor current to a current command value corresponding to the torque command value received from the vehicle ECU, so as to cause the motor to generate a torque corresponding to the torque command value. Therefore, in the event that the traction load has abruptly changed as described above, it is necessary to modify the torque command value produced from the vehicle ECU so as to compensate a caused difference. However, in this case, there is a significant delay in time (approximately 20 ms) required for calculations performed in the vehicle ECU and in the motor control apparatus and also for mutual communications between them. As a result, the motor speed suddenly changes and the drivability will be worsened.